Grease compositions

ABSTRACT

The invention relates to a grease composition having a base oil and a thickener that includes hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group. The hydrophilic metal oxide particles have a BET specific surface area of at least 10 m 2 /g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm. The amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition. The invention further relates to methods for manufacturing the grease composition, and the use of the grease composition for lubricating bearings, gears and couplings.

FIELD OF THE INVENTION

The present invention relates to grease compositions, methods for manufacturing the grease compositions, and the use of the grease compositions for lubricating bearings, gears and couplings.

BACKGROUND OF THE INVENTION

Grease compositions are widely used for lubricating bearings and other structural components. A grease is an essential product to reduce, for example, wear, friction, running temperatures and energy losses. Greases are materials which comprise a base oil that is thickened with a metal soap, and they are usually prepared by reacting a metal hydroxide with a fatty acid in the presence of the base oil. Conventional metal soap greases require an energy intensive grease cooking and milling process in order to achieve proper thermo-mechanical stability. Conventional metal soap greases can still be sensitive to poor thermo-mechanical stability and can require additional treatments. It is known to improve further the stability, and thus the lubricating capacity, of conventional greases by adding solid additives during the thickening process. Examples of such solid additives are, for example, molybdenum disulfide, graphite, zinc oxide and/or a silica gel. The process of grease cooking and milling and additional treatments is relatively expensive because it is carried out at an elevated temperature and over a relatively long period of time. Moreover, the greases so prepared are still unsuitable for a variety of applications, and not all conventional greases are suitable for food and beverage processing applications.

Consequently, there is a need for greases which can easily be manufactured at low costs, which are stable and show highly attractive lubricating properties in terms of low friction performance. In addition, there is a need for greases that are biodegradable, environmentally benign and food compatible.

SUMMARY OF THE INVENTION

Object of the present invention is to provide grease compositions which show excellent lubricating properties such as grease life performance, corrosion wear and thermo and mechanical stability, and which can easily be manufactured at low costs and/or are more environmentally friendly. Surprisingly, it has now been found that this can be established when use is made of a base oil and a thickener which comprises hydrophilic metal oxide particles and a particular amine.

Accordingly, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group; wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the thickener comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

In particular, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds; wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

In particular, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles and one or more amines that contain at least one OH group; wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

In particular, the present invention relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and at least one OH group; wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

The grease compositions according to the present invention show an attractive low friction performance, whereas at the same time they can easily be manufactured at low costs and/or are more environmental friendly.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the attached drawing, showing some non-limiting exemplary embodiments of the invention, in which:

FIG. 1 is a chart showing the results of the test sample where the values of the Stribeck friction coefficient and the entrainment speed [mms-1] measurements obtained on the MTM rig are shown

DETAILED DESCRIPTION OF THE INVENTION

The thickener to be used in the present grease composition according to the present invention comprises one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group.

Preferably, the one or more amines are fatty acid amines. In the context of the present application fatty acid amines are defined as amines derived from fatty acids. It will be understood that fatty acids are aliphatic monocarboxylic acids derived from, or contained in esterified form in an animal or vegetable fat, oil or wax. In accordance with the present invention use can be made of natural and synthetic fatty acids. Suitably, the amine to be used in accordance with the present invention is a fatty acid that contains one or more unsaturated C—C bonds in which a NH2 group is introduced somewhere in the unsaturated fatty acid chain.

Primary, secondary, tertiary and cyclic amines exist. Organic amines include amino acids, trimethylamine, aniline and biogenic amines. Fatty amines have an amine attached to a hydrocarbon chain and the amines form part of oleochemical functional groups that are derived from plant and animal fats.

Several methods to make the amines to be used in accordance with the present invention are available. Amino acids are widely represented in biology and organic chemistry. The amino acid comprises functional groups of amine(s) and carboxylic acids. In biology the breakdown of amino acids forms amines. Many industrial and laboratory methods exist to form amines and many more methods to form different amines in combination with various starting amine ingredients and catalysts.

Amines can for instance be formed from ammonia in an alkylation reaction with alcohol in the presence of ammonia and in the presence of catalysts. Hydrogenation reduces nitriles to amines in the presence of a catalyst. Reaction of haloalkanes with ammonia and amines forms different type of amines. Lithiumaluminiumhydride can be used to reduce amides to amines. Many amines are produced from aldehydes and ketones via reductive amination, which can either proceed catalytically or stoichiometrically. Ammonium salts which can provide beneficial effects to the grease composition of the present invention can be formed from amines and halocarbons. The amines may also be formed by the hydrolysis of alkyl isocyanate, or by degradation of the acid amide with aid of hypochlorite, hypobromite, halogen, or in combination with a base, or the conversion of the corresponding acid azide with aid of an acid chloride with sodium azide resulting in amine hydrochloride, or reduction of a cyanide or of acid amide.

Commonly applied amines can originate from saturated and unsaturated fatty acids like lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, lauroleic acid, myristoleic acid, palmitoleic acid, gadoleic acid, erucic acid, ricinoleic acid, linoleic acid, linolenic acid, eleostearic acid, arachidonic acid, phenylstearylamine and clupanodic acid. The amines of the foregoing acids may be obtained by transformation to the acid amide followed by reduction with sodium in absolute alcohol. Other sources of mixed amines are known to the art.

The unsaturated fatty amines to be used in accordance with the presented invention can be prepared from ammonia of which one or two hydrogens are substituted by hydrocarbon chain of a length from 18 C-atom or more and having 1 to 3 unsaturated carbon bonds. Commercial unsaturated fatty amines are blends of fatty amine of various hydrocarbon chain length and comprising of 1 to 3 unsaturated carbon bonds. These blended compositions can have various wt. % of unsaturated fatty amines. These mixed fatty amines can be further processed to obtain the desired quantity of unsaturated amines and to control these amounts by applied processing techniques of decanting, steam distillation or other processing techniques. Examples of unsaturated fatty amines are oleylamine, linoleylamine, linolenylamine, arachidylamine, eleostearylamine, erucylamine, petroselenylamine, and palmitoleylamine.

The fatty acid from which the fatty amine can suitably be prepared comprises 2-24 carbon atoms. A suitable example is for instance oleic amine. Suitably, the amines are metal salts. When the amines are metal salts, the amount of metal (salt(s) is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the amines to be used in accordance with the present invention contain one or more unsaturated C—C bonds and/or at least one OH group. Suitably, the amines to be used in accordance with the present invention contain one or more unsaturated C—C bonds and at least one OH group. Suitably, the amines contain two or more unsaturated C—C bonds. Suitably, the amines contain two or more unsaturated C—C bonds and at least one OH group, preferably at least two OH groups.

Suitably, the unsaturated amines further include at least one OH-group. Suitable examples of such amines are ethyl hydroxy stearamine and bishydroxyethyl oleylamine, and diamines such as bishydroxyethyl oleylamine. Suitably, the one or more amines are fatty acid amines. The one or more unsaturated amines may suitably in addition contain at least one OH group, suitably at least two OH groups. Suitably, the one or more amines contain two or more unsaturated C—C bonds and at least one OH group. Suitably, the one or more amines are metal salts. The amines may contain an ester group.

The metal in the metal salts is preferably an alkali metal or an alkaline earth metal of Groups 1 and 2 of the Periodic System of Elements, and bismuth. Suitable examples of metals include lithium, potassium, sodium, calcium, aluminium, rubidium, cesium, francium, beryllium, strontium, barium, radium, bismuth and magnesium. In addition it is noted that the metal in the metal salt to be used can be a semi-metal such as borium. According to a preferred embodiment according to the present invention, the metal is an alkaline earth metal, most preferably calcium.

The thickener to be used in accordance with the present invention may in addition contain one or more metal salts of fatty acids.

The present invention therefore further relates to a grease composition comprising a base oil and a thickener which comprises a hydroxyl group containing metal compound, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group and one or more metal salts of fatty acids.

The present invention therefore preferably relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group and one or more metal salts of fatty acids, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

Suitable metal salts of fatty acids include metals salts of caprylic acid, pelargonic acid, capric acid, lauric acid, linderic acid, rayristic acid, tsuzuic acid, physetoleic acid, myristoleic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, 12-hydroxystearic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, linolic acid, linolenic acid, elaeostearic acid, tuberculostearic acid, arachidic acid, eicosadienic acid, eicosatrienic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, hexadocosanic acid, octadocosanic acid and erucic acid.

The one or more metal salts of fatty acids may be metal salts of different fatty acids. When use is made of two metal salts of different acids the first metal and the second metal may be the same metal or they may differ from each other. In another embodiment wherein use is made of two metal salts of fatty acids, the fatty acid of the first metal salt and the fatty acid of the second metal salt may be the same fatty acid or they may differ from each other. When two different metal salts of fatty acids are used, the at least first and second metals will not be the same metal when the fatty acid of the first metal salt and the fatty acid of the second metal salt are the same fatty acids, and vice versa. Suitably, the fatty acid of the first metal salt and the fatty acid of the second metal salt comprise a different number of carbon atoms. Preferably, the fatty acid of the first metal comprises 2-16 carbon atoms and the fatty acid of the second metal salt comprises 20-24 carbon atoms. Suitably, the fatty acid of the first metal salt is butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid or palmitic acid, preferably caproic acid or caprylic acid. Suitably, the fatty acid of the second metal salt is arachidic acid, behenic acid or lignoceric acid. Such a grease composition is particularly attractive in low speed applications such as mining and cement applications. Preferably, the thickener includes in addition to the one or more amines a metal salt of stearic acid, 12-hydroxy stearic acid and/or oleic acid. More preferably, the metal salt is 12-hydroxy stearic acid, preferably in combination with a metal salt of stearic acid and/or a metal salt of oleic acid. The thickener may apart from the one or more metal salts of fatty acids also contain one or more fatty acids. Preferably, the thickener contains in addition a metal salt of 12-hydroxy stearic acid, stearic acid or oleic acid also 12-stearic acid, stearic acid or oleic acid. The metal salts of fatty acids may contain an OH group, amine group and/or ester group.

The present invention preferably relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group and one or more fatty acids, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the thickener comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

Suitable fatty acids that can be used include caprylic acid, pelargonic acid, capric acid, lauric acid, linderic acid, rayristic acid, tsuzuic acid, physetoleic acid, myristoleic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, 12-hydroxystearic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, linolic acid, linolenic acid, elaeostearic acid, tuberculostearic acid, arachidic acid, eicosadienic acid, eicosatrienic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, hexadocosanic acid, octadocosanic acid and erucic acid.

When use is made of two or more different fatty acids the fatty acids suitably comprise a different number of carbon atoms. Preferably, a first fatty acid comprises 2-16 carbon atoms and a second fatty acid comprises 20-24 carbon atoms. Suitably, the first fatty acid is butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid or palmitic acid, preferably caproic acid or caprylic acid. Suitably, the second fatty acid is arachidic acid, behenic acid or lignoceric acid. Such a grease composition is particularly attractive in low speed applications such as mining and cement applications. In another attractive embodiment of the present invention, the grease composition comprises two different fatty acids, wherein the fatty acids both comprise 18 carbon atoms. Suitably, the two fatty acids are selected from stearic acid, oleic acid and 12-hydroxy stearic acid. Preferably, the first fatty acid is 12-hydroxy stearic acid and the second fatty acid is stearic acid. The 12-hydroxy stearic acid will be able to form covalent bonds with OH-groups (silanol) of amorphous hydrophilic fumed silicon oxide resulting in a very attractive performance of the grease composition in terms of thermal mechanical stability.

When one or more metal salts of fatty acids and/or one or fatty acids are present, preferably at least one metal salt of a fatty acid or fatty contains one or more unsaturated C—C bonds and at least one OH group.

The present invention also relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, and one or more esters, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

The esters to be used suitably contain one or more unsaturated C—C bonds and/or at least one OH group. Suitable esters include unsaturated esters such as methyl oleate ester and ethyl linoleate ester; saturated diesters such as dioctyl sebacate ester, diisooctylsebacate ester and dioctyl adipate ester; and OH-group containing esters such methyl-12-hydroxystearate ester 9-octadecenoic acid, 12 hydroxy methyl ester and hydroxy palmitic ester. The diesters to be used may also contain one or more unsaturated C—C bonds. The esters to be used in accordance with the present invention include branched and unbranched esters. Suitable esters include unbranched and branched alkylated carboxylate esters, as well as triglycerides, in particularly unsaturated triglycerides. Suitably, the one or more esters contain one or more unsaturated C—C bonds. Preferably, the one or more esters contain one or more unsaturated C—C bonds and at least one OH group. Suitably, the one or more esters are diesters. Suitably, the one or more esters contain two or more unsaturated C—C bonds. Suitably, the one or more esters contain at least two OH groups. Suitably, the one or more esters contain at least two unsaturated C—C bonds and at least one OH group. Suitably, the one or more esters contain at least two unsaturated C—C bonds and at least two OH groups. Suitably, the one or more esters are metal salts. The esters may containing an amine group and/or amide group. Suitably, the thickener comprises in addition one or more sulphonates, sulphates, phosphates and/or phosphonates. When the one or more esters are metal salts, the amount of metal (salt(s) is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

The present invention in particular relates to a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group and one or more amides, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the thickener comprises in addition one or more metal salts such as metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.

Suitably, the amides to be used in accordance with the present invention contain one or more unsaturated C—C bonds and/or at least one OH group. Suitably, the amides to be used in accordance with the present invention contain one or more unsaturated C—C bonds and at least one OH group. Suitably, the amides contain one or more unsaturated C—C bonds and at least one OH group. Suitably, the amides contain two or more unsaturated C—C bonds. Suitably, the amides contain two or more unsaturated C—C bonds and at least one OH group, preferably at least two OH groups. The amides may contain an ester group.

Suitable amides that contain one or more unsaturated C—C bonds include unsaturated amides such as oleamide and linoleamide; diamides such as ethylene bis stearamide, hydroxy ethyl ethylene bis oleamide, ethylene bis-12-hydroxystearamide and bishydroxethyl oleylamine; and OH-group containing amides such as hydroxy ethyl ethylene bis oleamide, ethylene bis-12-hydroxystearamide.

Preferably, the unsaturated amides are unsaturated fatty acid amides, more preferably the amides are metal salts of unsaturated fatty acid amides.

The present invention preferably provides a grease composition comprising a base oil and a thickener which comprises crystalline hydrophilic metal oxide particles, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μm, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition. Suitably, the additional one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides contain one or more unsaturated C—C bonds and/or at least one OH group. Preferably, the additional one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides contain one or more unsaturated C—C bonds and at least one OH group. The one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides may be any of the fatty acids, fatty acids, esters and amines as described hereinabove.

The present invention preferably provides a grease composition comprising a base oil and a thickener which comprises hydrophilic metal oxide particles, one or more metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates, and one or more amines that contain one or more unsaturated carbon-carbon bonds and/or at least one OH group, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic metal oxide particles have a mean particle size of 5 nm to 900 μm, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease.

The grease compositions according to the present invention are preferably non-hydroxide grease compositions. Non-hydroxide grease compositions in accordance with the present invention do not contain impurities such as excess amounts of hydroxide which are normally present in greases that are prepared in conventional lithium and calcium soap manufacturing processes. The non-hydroxide grease compositions according to the present invention are suitably substantially free of free hydroxide ions and/or metal hydroxide. Preferably, the present non-hydroxide grease compositions contain less than 0.2% by weight, and more preferably less than 0.1% by weight of free hydroxide ions and/or metal hydroxide, based on the total weight of the grease composition. Preferably, the present non-hydroxide grease compositions are substantially free of free hydroxide ions and/or metal hydroxide. Preferably, the present grease compositions contain less than 0.2% by weight, and more preferably less than 0.1% by weight of metal hydroxide, based on the total weight of the grease composition. Most preferably, the present non-hydroxide grease compositions are completely free of metal hydroxide. It will be understood that OH-groups present on the hydrophilic metal oxide particles or in an fatty acid such as 12-hydroxy stearate or the metal salt of such an fatty acid are not to be considered free hydroxide ions since they are bonded to silicon atoms or to a carbon atom of the fatty acid. The thickener to be used in accordance with the present invention is suitably a non-saponified thickener.

The present invention further provides a grease composition comprising a base oil and a thickener which comprises hydrophilic silicon oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the hydrophilic silicon oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic silicon oxide particles have a mean particle size of 5 nm to 900 μm, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

The present invention further provides a grease composition comprising a base oil and a thickener which comprises hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles have a BET specific surface area of at least 10 m2/g and at least 80% of the hydrophilic titanium oxide particles and/or hydrophilic aluminium oxide particles have a mean particle size of 5 nm to 900 μm, and wherein the amount of the thickener is 0.1-40% by weight, based on the total weight of the grease composition.

The nature of the base oil to be used in accordance with the present invention is not essential. The base oil may be selected from the group consisting of mineral base oils and synthetic base oils. Mineral base oils are derived from crude oils and are either formulated on the basis of aromatic, paraffinic and/or naphthenic base oils. Further, a wide range of synthetic base oils is known and they include esters, poly-alpha-olefins, polysiloxanes and the like.

The base oil to be used in accordance with the present invention may comprise a base oil blend. Suitably, blends of mineral base oils and synthetic base oils may be used. The base oil in this invention is one which may ordinarily be used as the base oil of a lubricating oil or as the base oil of a grease, and there are no special restrictions. As examples mention may be made of mineral oils, synthetic oils, animal and plant oils, and mixtures thereof. In particular it is possible to use, singly or as mixtures, base oils which belong to Group I, Group II, Group III, Group IV and so on of the API (American Petroleum Institute) base oil categories. Group I base oils include, for example, paraffinic mineral oils obtained by a suitable combination of refining processes such as solvent refining, hydrorefining, and dewaxing in respect of lubricating oil-o fractions obtained by atmospheric distillation of crude oil. Group II base oils include, for example, paraffinic mineral oils obtained by a suitable combination of refining processes such as hydrorefining and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. Group II base oils refined by hydrorefining methods such as the Gulf Company method have a total sulphur content of less than 10 ppm and an aromatic content of not more than 5% and so are suitable for this invention. Group III base oils and Group 11+ base oils include paraffinic mineral oils manufactured by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and base oils refined by the Mobil wax isomerisation process. These too are suitable for use in this invention. Concrete examples of synthetic oils include polyolefins, polyoxyalkylene glycols such as polyethylene glycol or polypropylene glycol, esters such as di-2-ethylhexyl sebacate or di-2-ethylhexyl adipate, polyol esters such as trimethylolpropane esters or pentaerythritol esters, perfluoroalkyl ethers, silicone oils, polyphenyl ethers, and so on. The aforementioned polyolefins include polymers of various olefins or hydrides thereof. Any olefin may be used, and as examples mention may be made of ethylene, propylene, butene and [alpha]-olefins with five or more carbons. In the manufacture of polyolefins, one of the aforementioned olefins may be used singly or two or more may be used in combination. Particularly suitable are the polyolefins called poly-[alpha]-olefins (PAO). These are base oils of Group IV. GTL (gas to liquid) base oils synthesised by the Fischer-Tropsch method of converting natural gas to liquid fuel have a very low sulphur content and aromatic content compared with mineral oil base oils refined from crude oil and have a very high paraffin constituent ratio, and so have excellent oxidative stability, and because they also have extremely small evaporation losses, they are suitable as base oils for this invention. As typical examples of animal and plant oils mention may be made of castor oil and rape-seed oil. The various aforementioned oils may be used singly or in mixtures for the base oil. The aforementioned examples are listed singly but the invention is not limited thereby.

Preferably, the base oil or the base oil blend to be used in accordance with the present invention has a kinematic viscosity in the range of 1 to 60 000 cSt at a temperature of 40° C. according to DIN 51562/1. Suitable base oils include ISO VG 68, ISO VG 46, ISO VG 32, ISO VG 22, ISO VG 15 and ISO VG 10 oils.

The hydrophilic metal oxide particles to be used in accordance with the present invention can be derived from titanium oxide, aluminium oxide and silicon oxide. Preferably, the hydrophilic metal oxide particles are hydrophilic silicon oxide particles. The metal oxide particles may be crystalline metal oxide particles or amorphous metal oxide particles. Preferably, the silicon oxide particles are amorphous silicon oxide particles. The amorphous silicon oxide may contain various amounts of water, implying that it may comprise silicic acid. In this respect it is noted that silicic acid is a general name for a group of chemical compounds, oligomers and polymers consisting of silicon, hydrogen, and oxygen. According to a preferred embodiment of the present invention, the amorphous silicon oxide particles are derived from an amorphous hydrophilic silicon oxide. More preferably, they are derived from an amorphous fumed silicon oxide. Most preferably, the silicon oxide particles are derived from an amorphous hydrophilic fumed silicon oxide. Fumed silicon oxide is an exceptionally pure form of silicon oxide made from silica tetrachloride as a starting material, as is well known in the art. Suitable sources for the fumed silicon oxide are Aerosil® which is commercially available from Evonik Industries (formerly known as Degussa) or Cap-o-Sil® which is commercially available from Cabbot Corporation. Preferably, silicon oxide particles have an average size in the range of from 5-100 microns and have a BET specific surface area in the range of from 5-100 m2/g.

In accordance with the present invention also mixtures of different hydrophilic metal oxide particles can be used. For example a mixture of hydrophilic titanium oxide particles and hydrophilic aluminium oxide particles can be used.

Suitably, the hydrophilic metal oxide particles have a BET specific surface area of at least 50 m2/g, more preferably at least 75 m2/g, yet even more preferably at least 100 m2/g, even yet more preferably at least 125 m2/g and most preferably at least 150 m2/g Although is it preferred that the BET specific surface area is as high as possible, it will usually not be higher than 500 m2/g Methods for determining the BET specific surface area are well known in the art.

In some embodiments of the present invention, the hydrophilic metal oxide particles have a BET specific surface area of less than 50 m2/g.

According to the present invention at least 80% of the hydrophilic metal oxide particles have a particle size of 5 nm to 900 μm. In some embodiments at least 80% of the hydrophilic metal oxide particles have a particle size of 5-50 nm, preferably of 5-40 nm, more preferably of 10-40 nm and most preferably of 20-40 nm. The total particle size distribution of the amorphous silicon oxide particles is preferably in the range of 1-50 nm.

The grease compositions according to the invention may additionally comprise other thickening components, e.g. polymers or other fatty compounds that contain one or more OH-groups and/or one or more unsaturated bonds and/or one or more ester groups and/or one or more aromatic groups. Such thickening components can suitably be present in an amount of less than 3% by weight, preferably less than 2% by weight, based on the total weight of the grease composition.

The grease compositions according to the present invention may comprise other additives to tailor its suitability to a certain use as is well known in the art. Such additives include anti-wear agents, anti-corrosion agents, rust inhibitors, friction modifiers, anti-oxidants, VI-improvers and the like as is well known by the person skilled in the art. As suitable examples of such additives sulphonates, sulphates, phosphates and/or phosphonates can be mentioned. Suitable sulphonates include for instance methyl ester sulphonate, sodium methyl ester sulphonate and calium sulphonate. Suitable sulphates include for example calcium sulphate, sodium dodecyl sulphate and sodium lauryl sulphate. Suitable phosphates include for instance calcium hydrogen phosphate and amine phosphate. Suitable phosphonates include for example calcium phosphonate ester and other phosphonate esters.

Other suitable additives include silanes, (alkylated) siloxanes, metal hydroxide silicates, silanols, hydrosilicates, metal bonded silicon compound such as Mg3(Si2O5)(OH)2. Examples of such additives are for instance polydimethyl siloxane oil, hexomethyldisiloxane, magnesium hydrosilicate and other phyllosilicates. As well as polymethylsilesquioxane, hydrated (metal)silicates, amorphous silica, and sythetic silica gels, which additives are all used to improve polymer performance. Such other additives can suitably be present in an amount in the range of from 1-40% by weight, preferably 2-20% by weight, based on the total weight of the grease composition. In case the grease composition contains a high amount of such other additives, e.g. 20-40% by weight, based on total weight of the grease composition, the grease composition will display paste-type properties. Hence, the grease composition in accordance with the present invention also includes pastes. The other additives may also include small amounts (less than 3% by weight, preferably less than 2% by weight, based on the total weight of the grease composition) of further metal salts of fatty acids, but such metal salts will not substantially contribute to the formation of the grease thickener. In that case the grease composition will contain more than four metal salts of different fatty acids. A number of grease compositions according to the present invention are hydroxide grease compositions.

The present grease compositions may in addition also contain a small amount of metal hydroxide. Suitable metal hydroxides include potassium hydroxide, aluminium hydroxide, calcium hydroxide, lithium hydroxide, sodium hydroxide, magnesium hydroxide barium hydroxide and bismuth hydroxide. Other suitable additives include polypropylene, polyethylene, urea, bentonite, and other greases such as (complex) greases and PTFE/PFPE greases.

A common disadvantage of conventionally manufacturing methods is that it requires a multiple number of hours for blending the various components, gelling and cooling of the grease composition. At a batch scale of about 1-5 metric tons, the total cooking (gelling) and cooling can take about four hours or more, whereas grease milling can require two or more hours. Usually, the total manufacturing time takes about eight hours. However, the grease compositions according to the present invention can be prepared in a very short manufacturing process, wherein blending, gelling and cooling is preferably performed within one hour, more preferably within half an hour period. The mechanical treatment, preferably grease milling, in accordance with the present invention for a 5 metric ton volume can require about two or two and a half hours. In addition, it is observed that conventional grease manufacturing processes are carried out at high temperatures, typically in the range of from 170-220° C., whereas the present grease composition can suitably be prepared at a temperature below 90° C., including room temperature.

The present invention also provides methods for preparing the present grease compositions. In accordance with the present invention the components of the present grease compositions can be mixed in any possible order of sequence. Preferably, the hydrophilic metal oxide particles and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group are subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment. Hence, (a) the hydrophilic metal oxide particles or the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group are subjected to a mechanical treatment and/or thermal treatment; (b) a mixture of the hydrophilic metal oxide particles and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group are subjected to a mechanical treatment and/or thermal treatment; or (c) a mixture of the base oil, the hydrophilic metal oxide particles and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group are subjected to a mechanical treatment and/or thermal treatment.

Preferably, the hydrophilic metal oxide particles, the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, or a mixture of these components and the hydrophilic metal oxide particles is before or after mixing with the other component(s) subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment.

In accordance with the present invention the entire amount of base oil to be used or parts of the base oil can, for example, be added at one or more stages of the process. Suitable embodiments of the present invention include:

Subjecting a mixture of hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group to a mechanical and/or thermal treatment, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters, and/or amides, followed by adding to the mixture so obtained the base oil and optionally any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, and a part of the base oil to a mechanical and/or thermal treatment, followed by adding to the mixture so obtained the remaining part of the base oil and optionally any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles, the one or more amines that contain one or more unsaturated C—C and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, and the base oil to a mechanical and/or thermal treatment, followed by adding to the mixture so obtained any further additives, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting a mixture of the base oil, the hydrophilic metal oxide particles and one or more amines, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, and optionally any further additives, to a mechanical and/or thermal treatment. Subjecting the hydrophilic metal oxide particles to a mechanical and/or thermal treatment, followed by adding one or more one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, to the hydrophilic metal oxide particles so obtained and subjecting the mixture so obtained subsequently to a mechanical and/or thermal treatment. The base oil and optionally any further additives are then added to the mechanically and/or thermally treated mixture and the grease composition so obtained is then subjected to a mechanical and/or thermal treatment.

Subjecting the hydrophilic metal oxide particles to a mechanical and/or thermal treatment, followed by adding the base oil, one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, and optionally any further additives, to the mechanically and/or thermally treated hydrophilic metal oxide particles, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment. Subjecting one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, to a mechanical and/or thermal treatment, followed by adding the base oil, the hydrophilic metal oxide particles and optionally any further additives to the at least one metal salt so obtained, and subjecting the grease composition so obtained to a mechanical and/or thermal treatment.

Subjecting one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, and optionally any of the hereinbefore described one or more fatty acids, metal salts of fatty acids, esters and/or amides, to a mechanical and/or thermal treatment of, followed by adding the hydrophilic metal oxide particles to the mechanically and/or thermally treated amine(s) and subjecting the mixture so obtained subsequently to a mechanical and/or thermal treatment. The base oil and optionally any further additives are then added to the mechanically and/or thermally treated mixture and the grease composition so obtained is then subjected to a mechanical and/or thermal treatment.

As indicated above, the grease composition may comprise any further additives. Such further additives can be added to one or more of the components at any stage of the preparation process of the grease composition.

In the process according to the present invention each of the components or any mixture of the components can be subjected to a mechanical and/or thermal treatment in any possible order of sequence. For example, all components can be added together after which the mechanical and/or thermal treatment is applied. One of the components (e.g. the hydrophilic metal oxide particles) can first be subjected to a mechanical and/or thermal treatment after which one other component(s) (e.g. the amine) or two or more other components (e.g. one or more of the amines and the base oil) can be added to the mechanically and/or thermally treated component, followed by subjecting the grease composition so obtained to a mechanical and/or thermal treatment. Alternatively, one of the components (e.g. the hydrophilic metal oxide particles) can first be subjected to a mechanical and/or thermal treatment after which one other component (e.g. an amine) can be added to the mechanically and/or thermally treated component, subjecting the mixture so obtained to a further mechanical and/or thermal treatment, followed by adding yet one or more other components (e.g. the base oil and an optionally another metal salt) to the mechanically and/or thermally treated mixture so obtained, and subjecting the grease composition thus obtained to a mechanical and/or thermal treatment. According to one embodiment of the present invention, the hydrophilic metal oxide particles are first subjected to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment. Subsequently, the hydrophilic metal oxide particles so obtained are mixed with the base oil and the one or more amines that contain one or more unsaturated C—C and/or at least one OH group to form a grease composition.

Hence, the present invention also relates to a method for manufacturing a grease composition according to the present invention, which method comprises the following sequential steps:

(a) subjecting the hydrophilic metal oxide particles) to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment; and (b) mixing the hydrophilic metal oxide particles so obtained with the base oil and one or more amines that contain one or more unsaturated C—C and/or at least one OH group to form a grease composition.

According to another embodiment of the present invention, the hydrophilic metal oxide particles are first mixed with the base oil and the one or more amines that contain one or more unsaturated C—C and/or at least one OH group to form a grease composition, whereafter the grease composition so formed is subjected to the mechanical treatment, the thermal treatment or to both the mechanical treatment and the thermal treatment.

Accordingly, the present invention also relates to a method for manufacturing a grease according to the present invention, which method comprises the following sequential steps: (a) mixing the hydrophilic metal oxide particles with the base oil and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group to form a grease composition; and (b) subjecting the grease composition so formed to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment.

The mechanical treatment is preferably a milling step which can be performed in any suitable milling apparatus, e.g. a high pressure homogeniser, a colloid mill, a three-roller mill (e.g. a three-roller mill) or a worm gear mill. Preferably, the milling apparatus is a worm gear milling apparatus. The milling step can be performed under inert conditions, i.e. in the absence of air or oxygen and/or in the absence of water (vapour). The thermal treatment is preferably a heating step. The heating step preferably involves heating at a temperature in the range of 30-120° C., more preferably 40-110° C. and in particular 45-90° C. In this heating step, the water content of the amorphous hydrophilic metal oxide particles is reduced, preferably to a water content of the hydrophilic metal oxide particles of less than 5% by weight, more preferably less than 1% by weight, even more preferably less than 0.5% by weight, yet even more preferably less than 0.25% by weight, based on the total weight of the hydrophilic metal oxide particles. The water content of the hydrophilic metal oxide particles is usually more than 0.01% by weight, based on the total weight of the hydrophilic metal oxide particles.

Most preferably, the grease composition is manufactured by optionally subjecting the hydrophilic metal oxide particles to a thermal treatment, preferably a heating step, to reduce the water content of the hydrophilic metal oxide particles, followed by mixing the hydrophilic metal oxide particles with the base oil and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group to form a grease composition, whereafter the grease composition so formed is subjected to a mechanical treatment, preferably a milling step.

As disclosed above, the grease composition according to the present invention comprises a base oil, hydrophilic metal oxide particles, more in particular silicon oxide particles, and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the amount of the amine (s) is 0.1-40% by weight, based on the total weight of the grease composition. Suitably, the amount of the hydrophilic metal oxide particles will be 0.1-20% by weight, preferably 1-5% by weight, based on the total weight of the hydrophilic metal oxide particles and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group. The skilled person will understand how such amounts can be realised starting from the respective starting materials.

According to a preferred embodiment of the present invention, the total amount of the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, based on the total amount of the hydrophilic metal oxide particles and the amines, is within a range of 0.1-30% by weight, preferably within the range of 0.1-20% by weight, based on the total amount of the grease composition The grease composition according to the present invention can be used in many applications. However, it is in particular useful for lubricating a bearing, preferably a rolling element bearing, e g. a spherical roller bearing, a taper roller bearing, a cylindrical roller bearing, a needle roller bearing, a ball bearing, and may also be used to lubricate a sliding or plain bearing It is furthermore very useful in coupling and gearing applications.

The grease compositions according to the present invention encompass NLGI (National Lubricating Grease Institute) grades ranging from NLGI grade 000 to NLGI grade 6. Preferably, the grease compositions according to the present invention have a dropping point of at least 70° C. up to about 200° C. according to ASTM D-2265. When used in low loading gearings, the grease composition has preferably a NLGI grade of 000 to 1. When used in high loading gearings, the grease composition has preferably a NLGI grade of 0 to 2. When used in bearings, the grease composition has preferably a NLGI grade of 1 to 4, more preferably a NLGI grade of 2 or 3 and most preferably a NLGI grade of 2.

EXAMPLES

The performance of four grease compositions has been tested on tribological and friction performance on the Ball-on-disc, the Mini Traction Machine, at Imperial College, London UK. In each case the test procedure consists of four steps, i.e. first a grease working step which is followed by three consecutive Stribeck step tests. Two grease samples from each of the four grease compositions have undergone the entire test procedure. These duplications were performed to monitor the repeatability of the test between two different tests carried out in the exact same conditions. The same ball and disc used for each of grease samples were cleaned prior to running of the tests and the test repeat. The tests were run with fresh grease.

The grease working step had the purpose of ensuring an even distribution of the grease and to prepare the same initial condition for each test, by shearing the grease in the same way and for the same time, before the start of the actual test. In Table 1, the test operating conditions during the grease working step and the Stribeck test steps are shown.

TABLE 1 Grease working Stribeck steps (2nd, step (1st step) 3rd, 4th steps) Load [N] 1 31 Max Hertz pressure [GPa] 0.31 0.96 Temperature [° C.] 60 60 Speed range [mm/s] 5 (constant) 5-1000 (in 50 log steps) SRR [%] 0 10 Time [min] 5 6 In the four test procedure steps, the following operating conditions were applied.

Step 1—Grease working step: a ball load of 1 N was applied on the disc resulting in Hertzian contact pressure of 0.31 GPa, and a constant speed of 5 mm/s, for 5 minutes.

Steps 2-4—The three consecutive Stribeck steps: a ball load of 31 N was applied on the disc resulting in a Hertzian contact pressure of 1 GPa, and the speed increased from 5 mms/s to 1000 mms/s at a slide-to-roll ratio (SRR) of 10%. This step was repeated three times to monitor the repeatability of the step within the same test, and to analyse the friction coefficient evolution after each step due to the grease thixotropic character.

A test sample of a grease composition according to the present invention was manufactured from a paraffinic mineral blend base oil of 120 cSt from Scharr, Tunap, and 10 wt. % calciumhydroxystearate from Barlocher, 2 wt. % calciumstearate from Barlocher, 3 wt. % aerosol from Evonik i.e. hydrophilic silicon oxide primary particles having a BET specific surface area of 175-220 m2/g and the primary particle size ranges typically between 7-25 nm, 1.2 wt. % triphenylphosphate from M. Volkholz, 2 wt. % disodiumsebacic acid from M. Volkholz, 0.5 wt. % alkylphosphateamine from Ciba, 0.5 wt. % from butylated triphenyl phosphorothionate from Ciba, 0.5 wt. % benzotriazole from Ciba, 2.5 wt. % triphenylphosphorothionate from Ciba, 2 wt. % ditertdodecylpolysulfide from Elf Atochem, 10 wt. % oleic acid-oleylamine from Croda. The grease has been composed by adding, mixing and milling in a 3-roller-mill for 30 minutes in total.

For comparison reasons, test sample of the present invention was compared with three reference greases of the following compositions:

(a) Li-1 comprising and a lithium salt as a grease thickener, and having a mineral base oil viscosity of 100 mm2/s at 40° C.; (b) Li-2 comprising a mineral base oil and lithium salt as a grease thickener, and having viscosity of 200 mm2/s at 40° C.; (c) CaSX-1 comprising a base oil blend of mineral and synthetic PAO base oil and calcium sulphonate and calcium salts as a grease thickener, and having of a viscosity of 80 mm2/s at 40° C.

In FIG. 1, the results of the test sample according to the invention and the three reference grease compositions are compared with each other, whereby the values of the Stribeck friction coefficient and the entrainment speed [mms-1] measurements obtained on the MTM rig are shown. The boundary, mixed and full film lubricating regimes are indicated in the FIGURE over the ranges of entrainment speeds.

From FIG. 1 it is clear that the test sample of the grease composition according to the present invention constitutes an improvement in terms of lubrication and friction when compared with the three reference grease compositions. 

1. A grease composition comprising: a base oil, and a thickener that provides hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m²/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition.
 2. The grease composition according to claim 1, wherein the one or more amines are fatty acid amines.
 3. The grease composition according to claim 1, wherein the amine in addition contains one or more unsaturated C—C bonds and at least one OH group.
 4. The grease composition according to claim 1, wherein the one or more amines contain two or more unsaturated C—C bonds.
 5. The grease composition according to claim 1, wherein the one or more amines are metal salts.
 6. The grease composition according to claim 1, wherein the thickener further comprises one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides.
 7. The grease composition according to claim 6, wherein the thickener further comprises one or more metal salts of fatty acids.
 8. The grease composition according to claim 6, wherein the one or more metal salts of fatty acids, one or more fatty acids, one or more esters and/or one or more amides contain one or more unsaturated C—C bonds and/or at least one OH group.
 9. The grease composition according to claim 1, further comprising one or more metal sulphonates, metal sulphates, metal phosphates and/or metal phosphonates.
 10. The grease composition according to claim 1, wherein the hydrophilic metal oxide are silicon oxide particles.
 11. The grease composition according to claim 10, wherein the silicon oxide is amorphous fumed silicon oxide.
 12. A method for manufacturing a grease composition having a base oil, and a thickener that provides hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m²/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition, the method comprises: mixing the base oil, the hydrophilic metal oxide particles and the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group in any possible order of sequence, and subjecting before or after mixing the hydrophilic metal oxide particles, the one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, or a mixture thereof, to a mechanical treatment, a thermal treatment or to both a mechanical treatment and a thermal treatment.
 13. A grease composition having a base oil, and a thickener that provides hydrophilic metal oxide particles and one or more amines that contain one or more unsaturated C—C bonds and/or at least one OH group, wherein the hydrophilic metal oxide particles have a BET specific surface area of at least 10 m²/g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm, and wherein the amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition used for lubricating a bearing, a gearing or a coupling. 